Hi Ben, no doubt someone with more experience will be along shortly but it could be chlorosis, in which case it would pay to check the ph of the compost. I’m guessing that during the recent dry warm spell the plant needed watering fairly regular. Maybe acidity has been washed out of the compost.
A quick Google says some blueberries like a ph of 5.0. You probably already know but ph is measured on a logarithmic scale of ten. That is to say neutral is 7 so 6 is ten times more acidic than 7. It then follows that 5 is ten times more acidic than 6 making 5 one hundred times more acidic than 7 (10 x 10).
So if your blueberry likes a ph of 5.0 that’s quite acidic compost and could easily be washed out of range.
Just for comparison, black coffee has a ph of around 5.0
Hope this helps

Carltonian Man wrote:Hi Ben, no doubt someone with more experience will be along shortly but it could be chlorosis, in which case it would pay to check the ph of the compost. I’m guessing that during the recent dry warm spell the plant needed watering fairly regular. Maybe acidity has been washed out of the compost.
A quick Google says some blueberries like a ph of 5.0. You probably already know but ph is measured on a logarithmic scale of ten. That is to say neutral is 7 so 6 is ten times more acidic than 7. It then follows that 5 is ten times more acidic than 6 making 5 one hundred times more acidic than 7 (10 x 10).
So if your blueberry likes a ph of 5.0 that’s quite acidic compost and could easily be washed out of range.
Just for comparison, black coffee has a ph of around 5.0
Hope this helps

I've had a google for pictures of chlorosis of blueberry bushes and the symptoms seem very similar. I'll try adding more acidic compost to the top of the pot and hope that watering will wash it down to the roots.